DENVER -- Jets packed with people took off from Oak Harbor, Wash., and Salt Lake City yesterday in a simulated hijacking training exercise designed to improve coordination among American and Canadian agencies.

Fighter jets from the North American Aerospace Defense Command scrambled to respond to the simulated hijackings and were to run through several hypothetical scenarios, including one that involved shooting down the planes.

"We're prepared to do it, trained to do it, and ready to do it, but we'd much rather it be the source of last resort," said Marine Maj. Mike Snyder, a NORAD spokesman. "But make no mistake, we're ready to do it."

The exercise, involving more than 1,500 personnel from the United States and Canada, began about 6 a.m. The hijacking scenarios began shortly thereafter.

One plane, a Delta Air Lines 757, took off from Salt Lake City and was headed to Elmendorf Air Force Base in Anchorage, Alaska.

The other was a Navy C-9 airlifter, acting as another airliner, which traveled from Whidbey Island Naval Air Station at Oak Harbor to Vancouver, B.C., International Airport.

Both were packed with military personnel acting as civilian passengers. NORAD planned to run through a number of scenarios that would end with the planes landing. Once that occurred, law enforcement on the ground were to run through scenarios dealing with the hijackers from there.

The exercise was the latest training in the annual Amalgam Virgo exercises.

Last year's exercise involved testing defenses against a cruise missile attack on the Florida panhandle.

The 2002 scenario was planned before the Sept. 11 terrorist attacks, but Snyder said the events of that day helped officials fine-tune plans for the exercise. There were no plans for live firing.

Snyder said the exercise's chief use would be helping other agencies coordinate their response because NORAD has had so much practice since Sept. 11.

The defense command has flown 22,000 sorties under Operation Noble Eagle and conducted more than 300 so-called aviation events, where fighter jets responded to worries over small or commercial aircraft to determine their intent.

"NORAD is very well trained and exercised regarding this particular scenario," Snyder said.